Automated transmission systems such as auto shift gearboxes (ASG) and parallel shift gearboxes (PSG) that comprise a single or multiple shaft transmission are known in the field of motor vehicle technology. To change the transmission ratio, i.e., to shift gears in such a transmission, an idler gear of the current gear speed, i.e., the actual gear, is separated from the transmission input shaft and an idler gear of the desired gear, i.e., the target gear, is connected to the transmission input shaft in a form-fitting manner. However, due to the transmission ratio difference, there is a rotational speed difference between the transmission input shaft of the idler gear and the idler gear to be shifted to; a fact which precludes a form-fitting connection without gear noises such as creaking. For reasons of comfort, synchronization devices such as locking synchronizations are used to synchronize the rotational speed difference between the idler gear and the idler gear shaft.
The operation of the synchronization device may, for instance, be subdivided into five phases of the synchronization process.
In a first phase, an approximate synchronization is achieved wherein a movement of a switching sleeve that is connected to the idler shaft so as to be fixed against rotation but displaceable in the axial direction presses a synchro ring against the friction cone of an idler gear clutch body via thrust pieces. Due to the existing rotational speed difference between the clutch body and the switching sleeve the synchro ring is screwed into the stop.
In the second phase, the actual synchronization takes place. In the process, the switching spline of the switching sleeve is pressed against the roof chamfers of the synchro ring via its roof chamfers at a synchronization force. In this manner the resultant moment of friction accelerates or decelerates the idler gear. As long as there is a rotational speed difference, the moment of friction will always be greater than the moment of spline so that the synchronization device locks.
In a third phase, the synchro ring is rotated backwards to unlock the synchronization device.
In a fourth phase, the clutch body is rotated and thus causes the idler gear to rotate in a way to allow the switching sleeve to mesh.
Finally, in a fifth phase a form-fitting connection between the splines is created by completely meshing the switching spline with the clutch body.
In order to achieve optimum synchronization, a particularly soft initial approximate synchronization at a limited synchronizing force and at a suitable speed is required to avoid too sharp an increase of the moment of friction and to prevent the synchro ring from hitting hard against the stop. Otherwise, especially at low rotational speed differences, the synchronization may result in switching noises that may influence the power take-off.
In addition, the synchronizing force needs to be chosen to be sufficiently high to ensure suitably short synchronization periods depending on the rotational speed difference to be synchronized. Especially in auto shift gearboxes, a prolonged synchronization period has a negative effect on the switching convenience because of the extended interruption of the tractive force. Moreover, an increased energy input may damage the synchronization device.
Moreover, a sufficiently high synchronizing force is necessary to ensure a quick locking and meshing process. If this process takes too long, a new rotational speed difference may occur and may again cause meshing noise.
In order to meet these requirements in auto gearbox systems, the individual phases of the synchronizing process, in particular the locking and unlocking of the synchronizing device, need to be clearly distinguished. In general, due to the costs involved, gearbox systems operated by electric motors have dispensed with sensors to determine the initial gear speed and the shift finger force. Thus it is impossible to determine by sensors either the beginning of the synchronization, i.e., the locking, or the end of the synchronization, i.e., the unlocking, based on the input gear speed in correlation with the target input gear speed in the gear to be shifted to resulting from the vehicle speed and the total gear ratio or based on the switching force progression.
Thus it has become known in the field of vehicle technology to determine these phases based on the change of the condition of movement of the gearshift actuation in the shifting direction. For this purpose, the shifting sleeve is moved towards synchronization at a predetermined speed as a function of the target synchronizing force and a limited approximate synchronization force. A functional correlation can be given under the condition that the kinetic energy stored in the movement in the actuator by the inert mass relating to the shift finger is completely transmitted as potential energy to the stiffnesses reduced to the shift finger with the spring rate. If the shifting sleeve is retarded by a certain amount, a locking can be detected and the synchronizing force can be applied statically. In an analogous manner, the unlocking can be detected by an acceleration of the shifting sleeve by a certain amount.
The published German Patent Application No 10 2005 054 623 A1 discloses a synchronizing process at a constant synchronizing force that is selected as a function of the gas pedal, gear and rotational speed difference at the beginning of the shifting process. In situations of low loads, this synchronizing force is selected to be very small to keep the noise created at starting the synchronization unit at a comfortable level. At higher loads, the synchronizing force is selected to prevent the synchronizing process in the current situation from appearing as an uncomfortable jolt and at the same time to keep the synchronizing period as short as possible.
The start up of the synchronization unit occurs in a speed-controlled way at a shifting actuator speed that is selected to cause the applied constant synchronizing force to occur upon impacting on the synchronization unit. While the rotational speeds are synchronized, the shifting actuator is operated in a power-controlled way via the current. The resultant synchronizing force, however, is reduced by the friction of the system. Thus the actual synchronizing force may be very low, causing the synchronizing period to be very long.
If the synchronizing force is too high, undesirable noise at the beginning of the synchronizing process is the result. If the synchronizing force is too small, the synchronizing process takes a very long time.
To make sure that synchronizing takes place at all, an expected synchronization duration is calculated from the nominal synchronizing force, the rotational speed difference to be synchronized, and from gear-dependent parameters. Once this time has elapsed, the synchronizing force is increased. However, this is an emergency strategy which causes the synchronizing force to increase relatively late and potentially too much.